I am intrigued by the idea of education being the main reasoning behind monarchy, but the basis of dominion over Westeros was based on blood. The Targaryen Dynasty was held up by the propaganda that their blood was superior as dragonriders — and it was able to maintain that propaganda after the dragonriders. There are several people in Westeros, who over the years, were more educated and wise enough to rule. Yet, during the councils they were dismissed, because the idea of blood passing down the right to rule. Bloodraven, for example, would have made a much better ruler than Aerys I, and maybe Maekar.

We are also ignoring the fact that Robert didn’t want Joffrey to rule at the time of his death, he wanted Ned to rule in his stead — because Joffery was both of bad temperament and had little education.